The present invention relates to an engine, and more particularly, to a method and apparatus for engine ignition control.
The ignition timing of an engine substantially influences the performance of the engine and therefore has to be controlled precisely, cylinder by cylinder. Ignition timing is indicated by the rotation angle of the crankshaft with reference to TDC (Top Dead Center) during a piston stroke. The rotation angle of the crankshaft is detected by a crank-position sensor (CPS). A crank-position sensor includes a toothed gear and a magnetic sensor that generates pulse signals in response to the rotation of the teeth. This toothed gear is also sometimes a toothed ring that is placed about a rotating member of the crankshaft. The teeth are uniformly displaced except where a tooth is intentionally left out. A tooth or teeth are intentionally deleted from the toothed gear so the missing tooth region can be used to find a specific angular position on the crankshaft.
The resolution of the crank-position sensor depends on the number of teeth formed on the toothed gear. For example, if a toothed gear has 30 teeth (counting the missing teeth also), the angle between adjacent pulses of the toothed gear is 12xc2x0, and therefore the toothed gear has a resolution of 12xc2x0.
But the ignition timing must be controlled much more precisely than the resolution of this type of a crank-position sensor. Therefore, a timer is used to monitor the elapsed time between adjacent pulses and estimate when a desired between-pulse crank angle will arrive. For example, in the case of a toothed gear of 12xc2x0 resolution, to find 18xc2x0 BTDC (18xc2x0 Before Top Dead Center), the pulse from 24xc2x0 BTDC is detected and the remainder angle of 6xc2x0 is estimated by the timer. In practical use, however, the 36xc2x0 BTDC pulse is found (that is, the second pulse before the theoretically calculated one) and the remainder angle 18xc2x0 is estimated by the timer. This takes into account the fact that a small time period is needed to execute the timer instructions in a control unit.
Another point to be considered regarding ignition is that the ignition coil must supply a sufficiently large current to a spark plug. To do this, an ignition coil conducts current for a predetermined time period (referred to as xe2x80x9cdwell periodxe2x80x9d). The current begins at a point at which the dwell period starts (referred to as xe2x80x9cdwell-on pointxe2x80x9d). After the dwell period from the dwell-on point, the current is stopped, causing ignition in a cylinder. This is the starting time point of the ignition and is referred to as the xe2x80x9cignition timingxe2x80x9d. The dwell angle is the crank angle change corresponding to the dwell period. To keep the dwell period to a specific value, dwell angle must be constantly re-calculated because the dwell angle varies in response to engine speed.
Therefore, the Dwell-On timing as well as the ignition timing must be precisely controlled based on the crank angle obtained by the crank-position sensor, and a lot of research regarding ignition control of an engine is related to increasing precision and accuracy thereof.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art.
A preferred embodiment of an engine ignition control apparatus includes: a crank-position sensor for generating a pulse signal at each rotation angle of a crankshaft of the engine except for one or more missing pulses; an engine speed detector for detecting engine speed; an ignition coil driven by an electric current for Dwell-On and Ignition-On activation, said ignition coil generating a voltage for ignition of the spark plug under said Ignition-On activation; and an electric control unit for controlling said Dwell-On and Ignition On activation of the ignition coil based on the pulse signal and the engine speed. The electric control unit executes a set of instructions including instructions for each step of an ignition control method of an engine according to the present invention.
An exemplary ignition control method according to an embodiment of the present invention includes: calculating a dwell angle and an ignition angle of a reference cylinder based on an engine speed; calculating a first number of pulses and a first timer-monitored angle corresponding to a pre-Dwell-On period with regard to the reference cylinder, the pre-Dwell-On period being a period from occurrence of a first reference pulse to a Dwell-On timing with regard to the reference cylinder; comparing the first number of pulses with a predetermined number corresponding to 180xc2x0 of crank angle; determining an ignition cylinder based on the comparison of the first number with the predetermined number; and actuating ignition of a spark plug of the ignition cylinder based on the first number of pulses, the first timer-monitored angle, and the ignition angle of the reference cylinder.
The first reference pulse is preferably one of a secondly occurring pulse after a missing pulse of a crank-position sensor and a pulse having a 180xc2x0 angular difference thereto.
In a further preferred embodiment, said calculating a first number of pulses and a first timer-monitored angle includes: comparing a remainder of a first operation with a reference angle, the first operation being an operation of dividing an angular difference acquired by subtracting the dwell angle and the ignition angle from a BTDC angle of the first reference pulse by an angular difference between adjacent pulses; determining, when the remainder of the first operation is greater than the reference angle, the first number of pulses as a quotient of the first operation and the first timer-monitored angle as the remainder of the first operation; and determining, when the remainder of the first operation is not greater than the reference angle, the first number of pulses as a quotient of the first operation subtracted by 1 and the first timer-monitored angle as the remainder of the first operation plus the angular difference between adjacent pulses.
The reference angle is preferably less than the angular difference between adjacent pulses and greater than an angle corresponding to a required time for a timer to be is activated. In practical use, the reference angle may preferably be set to about 5xc2x0.
In another further embodiment, said determining an ignition cylinder based on the comparison determines the ignition cylinder as the reference cylinder when the first number is not greater than the predetermined number, and as another cylinder otherwise.
In a further preferred embodiment, said actuating ignition of a spark plug of the ignition cylinder includes: reducing the first number of pulses by the predetermined number when the ignition cylinder is different from the reference cylinder; counting the first number of pulses from occurrence of the first reference pulse; monitoring by timer for the first timer-monitored angle after said counting the first number of pulses; and actuating Dwell-On of an ignition coil of the ignition cylinder when the first timer-monitored angle elapsed.
In a further preferred embodiment, said actuating ignition of a spark plug of the ignition cylinder further includes: determining if a determination state of said determining ignition cylinder has been changed from a state such that the ignition cylinder is different from the reference cylinder to a state such that the ignition cylinder is the reference cylinder; and forcibly actuating Dwell-On of an ignition coil of said another cylinder when the determination state is determined to have been changed.
The exemplary method that is useful with the present invention preferably further includes: determining if a target pulse occurring after the first number of pulses after the first reference pulse lies in a missing pulse range, said missing pulse range covering a missing pulse; reducing the first number of pulses, when the target pulse lies in the missing pulse range, such that the target pulse no longer lies in the missing pulse range; and increasing the first timer-monitored angle by an angle obtained by multiplying a reduced number of the first number of pulses by the angular difference between adjacent pulses. The missing pulse range preferably includes the missing pulse and a firstly occurring pulse after the missing pulse.
In a further preferred embodiment, said actuating ignition of a spark plug of the ignition cylinder further includes: calculating a second number of pulses and a second timer-monitored angle corresponding to a pre-Ignition-On period with regard to the ignition cylinder, the pre-Ignition-On period being a period from occurrence of a second reference pulse to an Ignition-On point with regard to the ignition cylinder; counting the second number of pulses from occurrence of the second reference pulse; monitoring by timer for the second timer-monitored angle after said counting the second number of pulses; and actuating Ignition-On of the ignition coil of the ignition cylinder when the second timer-monitored angle has elapsed.
In a further preferred embodiment, said calculating a second number of pulses and a second timer-monitored angle includes: comparing a remainder of a second operation with a reference angle, the second operation being an operation of dividing an angular difference acquired by subtracting the ignition angle from a BTDC angle of the second reference pulse by an angular difference between adjacent pulses; determining, when the remainder of the second operation is greater than the reference angle, the second number of pulses as a quotient of the second operation and the second timer-monitored angle as the remainder of the second operation; and determining, when the remainder of the second operation is not greater than the reference angle, the second number of pulses as a quotient of the first operation subtracted by 1 and the second timer-monitored angle as the remainder of the second operation plus the angular difference between adjacent pulses.
The reference angle is preferably less than the angular difference between adjacent pulses and greater than an angle corresponding to a required time for a timer to be activated. In practical use, the reference angle may preferably be set to about 5xc2x0.
In a further preferred embodiment, said actuating ignition of a spark plug of the ignition cylinder further includes: determining if a determination state of said determining an ignition cylinder has been changed from a state such that the ignition cylinder is different from the reference cylinder to a state such that the ignition cylinder is the reference cylinder; and forcibly actuating, when the determination state is determined to have been changed, Ignition-On of an ignition coil of said another cylinder synchronously with said actuating Ignition-On of the ignition coil of the ignition cylinder.